Callen's former CIA partner, Tracey Keller, holds a Navy Recruitment Office hostage to get Callen's attention.
Tracey claims she is now working an undercover case for the FBI to stop an arms deal but several agents went rogue and got involved with the weapons deal.
Now someone is trying to kill her and she feels the only one she can trust is Callen. Callen is unsure if he can believe Tracey since the last time he saw her she almost got him killed, until a sniper outside the recruitment office tries to shoot Tracey.
FBI Agent White initially works with Sam to try and find the sniper who shot at Tracey but surveillance cameras show he was the one to take the shot after he killed an LAPD sniper.
Tracey tells the team that White and her former FBI partner where to meet with an international arms dealer, John Thomas Mason, today to give him SIM cards needed to activate the shipment of Spike missiles he recently stole; without the cards the missiles are useless.
Tracey meets White and ends up killing him; she claims in self-defense.
Callen decides he and Tracey must re-partner to take down Mason and recover the missiles. Mason takes the bait and makes the deal, transferring millions to an off-shore account, but a gun fight ensures when the team moves in.
Tracey begs Callen to let her go and in the heat of the moment Callen complies.
Tracey planned this chain of events from the beginning and Callen knew he couldn't trust her so he had Eric track her from the moment he let her go.
Callen finds her in the Cayman Islands and Tracey knows it's over the moment she sees him.